计及直流偏磁的保护用电流互感器仿真与实验分析  

Analysis of simulation and experiment on the characteristic of the current transformer used for protection affected by DC magnetic bias

作　　者：王振浩[1] 王学斌[1,2] 李国庆[1] 陈洪涛 陶平虎 

机构地区：[1]东北电力大学电气工程学院,吉林吉林132012 [2]国网甘肃省电力公司兰州供电公司,甘肃兰州730070 [3]国网吉林省电力公司松原供电公司,吉林松原138000 [4]国网甘肃省电力公司刘家峡水电厂,甘肃永靖731600

出　　处：《电力系统保护与控制》2015年第13期15-22,共8页Power System Protection and Control

基　　金：国家自然科学基金(51377016)~~

摘　　要：保护用电流互感器(Current Transformer,CT)对电力系统继电保护的动作特性影响很大。直流偏磁会对CT的传变特性产生影响,利用其T型等值电路推导出了直流偏磁条件下的励磁电流和磁通的表达式。通过PSCAD/EMTDC仿真软件对不同直流偏移系数条件下的CT传变特性进行仿真分析,结果表明,偏磁条件下CT的磁化曲线第三象限部分会减小,二次电流波形也会发生畸变,同时二次电流中谐波幅值也在增加,当偏磁电流增加到一定值时二次谐波将会大于三次谐波,随着直流偏移系数的增加各次谐波也呈线性增长,而基波幅值在减小。同时,设计了交流叠加直流的实验电路来模拟直流偏磁现象以对保护用CT的传变特性进行实验分析。实验结果表明,在偏磁条件下CT不能正确传变一次电流,在偏磁条件下CT二次电流有效值会减小,同时基波幅值也相应减小,而其余各次谐波的幅值呈线性增加,对角差的影响较电流误差而言更为严重。由此可见,直流偏磁改变了保护用CT的传变特性,对采用基波分量算法及谐波制动方案类型的保护构成严重威胁,降低继电保护的可靠性。The current transformer （CT） used for protection has a great effect on operation characteristics for protective relaying. Its transfer characteristics could beimpacted by DC bias and its excitation current and magnetic flux is derived by T-shaped equivalent circuit. Then the analysis of simulation on different DC offset ratio by means of PSCAD/EMTDC software. The simulation result shows that it will cause CT＇s magnetization curve in third quadrant decrease and its secondary current distortion meanwhile the harmonic of secondary current increase and when the DC offset coefficient increase to a certain value the second harmonic will be greater than the third harmonic, but the fundamental is reduced accordingly. And the transfer characteristic of protective CT could be analyzed by simulating DC bias with the designed AC superposed DC experiment circuit. The result of experiment shows that the CT can not transfer the primary current accurately on DC bias condition, the secondary effective current decreases on DC bias and the fundamental decreases and others harmonic increases, and the impact to the phase error more serious than current error. So, the protective CT＇s transfer characteristic is changed and it＇s a serious threat to protection used for fundamental algorithm and harmonic restraint scheme which can reduce the reliability of relay protection.

关 键 词：直流偏磁 电流互感器 励磁特性 谐波 幅值 

分 类 号：TM452[电气工程—电器] TM77